Rattlesnake
Rattlesnakes are a group of venomous snakes of the genera Crotalus and Sistrurus of the subfamily Crotalinae ("pit vipers"). There are 32 known species of rattlesnake, with between 65-70 subspecies, all native to the Americas, ranging from southern Alberta and southern British Columbia in Canada to Central Argentina. Rattlesnakes are predators who live in a wide array of habitats, hunting small animals such as birds and rodents. They kill their prey with a venomous bite, rather than by constricting. All rattlesnakes possess a set of fangs with which they inject large quantities of hemotoxic venom. The venom travels through the bloodstream, destroying tissue and causing swelling, internal bleeding, and intense pain. Some species, such as the Mojave Rattlesnake, additionally possess a neurotoxic component in their venom that causes paralysis and other nervous symptoms. The threat of envenomation, advertised by the loud shaking of the titular noisemaker ("rattle") at the end of their tail, deters many predators. However, rattlesnakes fall prey to hawks, weasels, king snakes, and a variety of other species. Rattlesnakes are heavily preyed upon as neonates, while they are still weak and mentally immature. Very large numbers of rattlesnakes are killed by humans. Rattlesnake populations in many areas are severely threatened by habitat destruction, poaching, and extermination campaigns. Rattlesnake bites are the leading cause of snakebite injuries in North America, and cause approximately 82% of fatalities. However, rattlesnakes rarely bite unless provoked or threatened; and if treated promptly, the bites are rarely fatal. Names Rattlesnakes receive their name from the rattle located at the end of their tails, which, when shaken, makes a loud rattling noise that deters predators or serves as a warning to passersby. The scientific name Crotalus derives from the Greek, κρόταλον, meaning "castanet". The name Sistrurus is the Latinized form of the Greek word for "tail rattler" (Σείστρουρος, Seistrouros) and shares its root with the ancient Egyptian musical instrument, the sistrum, a type of rattle. Ecology Range and habitat ), responsible for the majority of venomous snakebites in North America, coiled in defensive posture with rattle erect]] Rattlesnakes are native to the Americas, living in diverse habitats from Southwestern Canada to Central Argentina. The large majority of species live in the American Southwest and Mexico. Four species may be found east of the Mississippi river, and two in South America. In the United States, the state with the most forms of rattlesnakes is Arizona, with seventeen species and subspecies. Rattlesnakes are found in almost every type of habitat that is capable of supporting terrestrial ectothermic vertebrates; but individual species can have extremely specific habitat requirements, only able to live within certain plant associations in a narrow range of altitudes. Most species live near open, rocky areas. Rocks offer them cover from predators, plentiful prey (e.g. rodents, lizards, insects, etc. that live amidst the rocks), and open basking areas. However, rattlesnakes can also be found in a wide variety of other habitats including prairies, marshes, deserts, and forests. Rattlesnakes prefer a temperature range between 80 and 90°F (26-32°C), but can survive temperatures below freezing, recovering from brief exposure to temperatures as low as 4°F, and surviving for several days in temperatures as low as 37°F. Evidence has been collected to show the most probable ancestral area of rattlesnakes is the Sierra Madre Occidental region in Mexico. This same study found the most probable vegetation or habitat of the ancestral area to be pine-oak forests. Prey Rattlesnakes consume mice, rats, small birds and other small animals, playing an important ecological role by limiting the size of rodent populations, which prevents crop damage and stabilizes ecosystems. Rattlesnakes lie in wait for their prey, or hunt for it in holes. The prey are killed quickly with a venomous bite as opposed to constricting. If the bitten prey moves away before dying, the rattlesnake can follow it by its scent. When it locates the fallen prey, it checks for signs of life by prodding with its snout, flicking its tongue, and using its sense of smell. Once the prey has become incapacitated, the rattlesnake locates its head by odors emitted from the mouth. The prey is then ingested head-first, which allows wings and limbs to fold at the joints in a manner which minimizes the girth of the meal. The gastric fluids of rattlesnakes are extremely powerful, allowing for the digestion of bone as well as flesh. Optimal digestion occurs when the snake maintains a body temperature of between 80 and 85°F (25-29°C). If the prey is small, the rattlesnake will often continue hunting. If it was an adequate meal, the snake will find a warm, safe location in which to coil up and rest until the prey is digested. Rattlesnakes are believed to require at least their own body weight in water annually in order to remain hydrated. The method in which they drink depends on the water source. In larger bodies of water (streams, ponds, etc.) they will submerge their head and ingest water by opening and closing their jaw, which sucks in water. If drinking dew, or drinking from small puddles, they will sip the liquid either by capillary action or by flattening and flooding the lower jaw. Predators Newborn rattlesnakes are heavily preyed upon by a variety of species including ravens, crows, roadrunners, raccoons, opossums, skunks, coyotes and weasels, whipsnakes, kingsnakes, and racers. Neonates of the smaller Crotaline species are frequently killed and eaten by small predatory birds such as jays, kingfishers, and shrikes. Some species of ants in the genus ''Formica are known to prey upon neonates, and it is very likely that Solenopsis invicta (fire ants) do as well. On occasion, hungry adult rattlesnakes will cannibalize neonates. The small proportion (often as few as 20%) of rattlesnakes that make it to their second year are heavily preyed upon by a variety of larger predators including coyotes, eagles, hawks, owls, feral pigs, badgers, indigo snakes, and kingsnakes. The common kingsnake (Lampropeltis getula), a constrictor, is immune to the venom of rattlesnakes and other vipers, and rattlesnakes form part of its natural diet. Rattlesnakes sense kingsnakes' presence by their odor. When they realize a kingsnake is nearby, they begin enacting a set of defensive postures known as "body bridging". Unlike its normal erect and coiled defensive-striking posture, the rattlesnake keeps its head low to the ground in an attempt to prevent the kingsnake from gaining a hold of it (the head being the first part of the rattlesnake that is ingested). The rattlesnake jerks its body about, while bridging its back upwards, forming an elevated coil which faces the kingsnake. The elevated coil is used to strike the attacker, and is also used to shield the head from the kingsnake. Anatomy Sensory organs ) with clearly visible facial pits]] Like all pit vipers, rattlesnakes have two organs that can sense radiation: their eyes, and a set of heat-sensing "pits" on their face that enable them to locate prey and strike towards it, based on the prey's thermal radiation signature. These pits have a relatively short effective range of approximately 1 ft, but nevertheless give the rattlesnake a distinctive advantage in hunting for warm-blooded creatures at night. Rattlesnake eyes, which contain a large number of rod cells, are well adapted to nocturnal use. However rattlesnakes are not exclusively nocturnal, and their vision is more acute during daylight conditions. Rattlesnakes also possess cone cells, which means that they are capable of some form of color vision. The rattlesnake eye lacks a fovea making it impossible for them to see sharply defined images. Instead, they mostly rely on the perception of movement. Rattlesnake eyes are capable of horizontal rotation, but they do not appear to move their eyeballs to follow moving objects. Rattlesnakes have an exceptionally keen sense of smell. They can sense olfactory stimuli both through their nostrils, and by flicking their tongue, which carries scent-bearing particles to the Jacobson's organ in the roof of their mouth. Like all snakes, rattlesnakes do not have external ear openings, and the structures of their middle ear is not as highly specialized as those of other vertebrates, such as mammals. Thus their sense of sound is not very effective. However, they are capable of sensing vibrations in the ground, passed via the skeleton to the auditory nerve. Fangs Rattlesnake fangs are connected by venom ducts to large poison glands near the outer edge of the upper jaw, towards the rear of the head. When the rattlesnake bites, muscles on the sides of the venom glands contract, which squeezes the venom through the ducts and into the fangs. When the fangs are not in use, they remain folded against the palate. Rattlesnakes are born with fully functioning fangs and venom, and are capable of killing prey at birth. Adult rattlesnakes shed their fangs every 6–10 weeks. At least 3 pairs of replacement fangs lie behind the functional pair. Venom Most species of rattlesnakes have hemotoxic venom, destroying tissue, causing necrosis and coagulopathy (disrupted blood clotting). In the U.S., some varieties of the Mojave rattlesnake (''C. scutulatus) also have a presynaptic neurotoxic venom component known as Mojave Type A toxin, which can cause severe paralysis. C. scutulatus is widely regarded as producing one of the most toxic snake venoms in the Americas, based on studies in laboratory mice. Rattlesnake venom is a mixture of 5-15 enzymes, various metal ions, biogenic amines, lipids, free amino acids, proteins, and polypeptides. It contains components designed to immobilize and disable the prey, as well as digestive enzymes which break down tissue to prepare for later ingestion. The venom is very stable, and retains its toxicity for many years in storage. Older snakes possess more potent venom, and larger snakes are frequently capable of storing larger volumes of it. Rattle